fix: REPL display, /compact panic, identity leak, DeepSeek reasoning, thinking blocks

Five interrelated fixes from parallel Hephaestus sessions:

1. fix(repl): display assistant text after spinner (#2981, #2982, #2937)
   - Added final_assistant_text() call after run_turn spinner completes
   - REPL now shows response text like run_prompt_json does

2. fix(compact): handle Thinking content blocks (#2985)
   - Added ContentBlock::Thinking variant throughout compact summarizer
   - Prevents panic when /compact encounters thinking blocks

3. fix(prompt): provider-aware model identity (#2822)
   - New ModelFamilyIdentity enum (Claude vs Generic)
   - Non-Anthropic models no longer say 'I am Claude'
   - model_family_identity_for() detects provider and sets identity

4. fix(openai): preserve DeepSeek reasoning_content (#2821)
   - Stream parser now captures reasoning_content from OpenAI-compat
   - Emits ThinkingDelta/SignatureDelta events for reasoning models
   - Thinking blocks included in conversation history for re-send

5. feat(runtime): Thinking block support across codebase
   - AssistantEvent::Thinking variant in conversation.rs
   - ContentBlock::Thinking in session serialization
   - Thinking-aware compact summarization
   - Tests for thinking block ordering and content

Closes #2981, #2982, #2937, #2985, #2822, #2821

rust/crates/api/src/providers/mod.rs

@@ -250,6 +250,19 @@ pub fn detect_provider_kind(model: &str) -> ProviderKind {
     ProviderKind::Anthropic
 }
 
+#[must_use]
+pub const fn model_family_identity_for_kind(kind: ProviderKind) -> runtime::ModelFamilyIdentity {
+    match kind {
+        ProviderKind::Anthropic => runtime::ModelFamilyIdentity::Claude,
+        ProviderKind::Xai | ProviderKind::OpenAi => runtime::ModelFamilyIdentity::Generic,
+    }
+}
+
+#[must_use]
+pub fn model_family_identity_for(model: &str) -> runtime::ModelFamilyIdentity {
+    model_family_identity_for_kind(detect_provider_kind(model))
+}
+
 #[must_use]
 pub fn max_tokens_for_model(model: &str) -> u32 {
     let canonical = resolve_model_alias(model);
@@ -484,8 +497,8 @@ mod tests {
     use super::{
         anthropic_missing_credentials, anthropic_missing_credentials_hint, detect_provider_kind,
         load_dotenv_file, max_tokens_for_model, max_tokens_for_model_with_override,
-        model_token_limit, parse_dotenv, preflight_message_request, resolve_model_alias,
-        ProviderKind,
+        model_family_identity_for, model_family_identity_for_kind, model_token_limit, parse_dotenv,
+        preflight_message_request, resolve_model_alias, ProviderKind,
     };
 
     /// Serializes every test in this module that mutates process-wide
@@ -544,6 +557,42 @@ mod tests {
         );
     }
 
+    #[test]
+    fn maps_provider_kind_to_model_family_identity() {
+        // given: each supported provider kind
+        let anthropic = ProviderKind::Anthropic;
+        let openai = ProviderKind::OpenAi;
+        let xai = ProviderKind::Xai;
+
+        // when: converting provider kinds to prompt model family identities
+        let anthropic_identity = model_family_identity_for_kind(anthropic);
+        let openai_identity = model_family_identity_for_kind(openai);
+        let xai_identity = model_family_identity_for_kind(xai);
+
+        // then: Anthropic stays Claude and OpenAI-compatible providers are generic
+        assert_eq!(anthropic_identity, runtime::ModelFamilyIdentity::Claude);
+        assert_eq!(openai_identity, runtime::ModelFamilyIdentity::Generic);
+        assert_eq!(xai_identity, runtime::ModelFamilyIdentity::Generic);
+    }
+
+    #[test]
+    fn maps_model_name_to_model_family_identity() {
+        // given: Anthropic, OpenAI-compatible, and xAI model names
+        let claude_model = "claude-opus-4-6";
+        let openai_model = "openai/gpt-4.1-mini";
+        let xai_model = "grok-3";
+
+        // when: detecting prompt model family identities from model names
+        let claude_identity = model_family_identity_for(claude_model);
+        let openai_identity = model_family_identity_for(openai_model);
+        let xai_identity = model_family_identity_for(xai_model);
+
+        // then: Anthropic stays Claude and OpenAI-compatible providers are generic
+        assert_eq!(claude_identity, runtime::ModelFamilyIdentity::Claude);
+        assert_eq!(openai_identity, runtime::ModelFamilyIdentity::Generic);
+        assert_eq!(xai_identity, runtime::ModelFamilyIdentity::Generic);
+    }
+
     #[test]
     fn openai_namespaced_model_routes_to_openai_not_anthropic() {
         // Regression: "openai/gpt-4.1-mini" was misrouted to Anthropic when